o-rings
you may have noticed in the pic that iwas running 2 o-rings over each side of the pack, if i were to do it agian i would add an extra post to each side (in the rear) so the o-rings could make a triangle pattern over the pack. whatever you do buy the o-rings tight, were they are tough to get on but not so much that they flex or tweak the chassis (it can happen). also, o-rings come with an oily coat on them (so they won't dry out) wipe that slick stuff off of them.